fix: temporary fix core-js dep for vue ui

close #2215

Author: yyx990803

packages/@vue/cli/package.json

@@ -29,6 +29,7 @@
     "chalk": "^2.4.1",
     "cmd-shim": "^2.0.2",
     "commander": "^2.16.0",
+    "core-js": "^2.5.7",
     "debug": "^3.1.0",
     "deepmerge": "^2.1.1",
     "download-git-repo": "^1.0.2",